Artificial arm with stepped-up wrist drive and automatic wrist lock



.May 19,1953

G. M. Mols RTFIK'JIAL ARM WITH IS'JPPED--UP WRIST DRTvE AND AUTOMATICWRIST Locx Filed July 14. 1951 3 ySheets-Sheet 1 G/cvir M Mor/J.,

vINVENTOR.

TTONEK G. M. MOTIS ARTIFICIAL ARM WITH STEPPED May 19, 1953 UP WRISTDRIVE AND AUTOMATIC WRIST Locx Filed Y.Juny 14, 1951 s sheets-sheet 2May 19 1953 G. M. MoTls ARTIFICIAL ARM WITH sTEPPEn-UP WRIST DRIVE ANDAUTOMATIC WRIST LOCK 3 Sheets-Sheet 3 Filed July 14, 1951 FiGA.

/lf Mor/5. .6M-@EPT INVENToR.

A [,'1 n BY /vll a :fro/@Mex Patented May 19, 1953 ARTIFICIAL, ARMv WITHS-'EEPPEDfUP WRIST DRIVE AND AUTOMATQ WRIST LOCK GilbertMetis,*NorthridgcifCalifa assignor to Northrop Aircraft, Inc.,Hawthorne, Calif., a corporation of California Application July 14,`1951, Seria-1 No. 236,787

12 claims. l

The present invention relates generally to `articial arms, and is moreparticularly concerned with below-elbow arms of the type wherein thehook or hand is rotatable and can be pronated and supinated by theforearm stump.

In artificial arms of this type, it is desirable to provide for somestep-up' of the rotationaly movement transmitted from the stumpl to thehook, owing to the fact that the pronation-supination movement of thestump is inversely proportional to its length', and' is usually notsuflicient to manipulate vthe hook to best advantage. One oi' theobjects of the invention, therefore, is to provide a new and improvedmechanism for rotating the wrist member from the stump with a steppedupratev ci movement.

Another important object of the invention is to provide an artcial armof the class described, wherein the wrist is locked automatically whenthe hook or hand is operated. The advantage of this feature is that itpreventsv the feed back of torsional loads from the hook or hand to. thestump socket, therebyA eliminating ,any tendency of the stump socket totwist on the stump, with attendant discomfort to the amputee. Suchtorsional loads may be due tothe pull of the control cable on the hookat a pointspaced radially outward from the axis oi rotation of thewrist, as in the case of external control hooks, yor they may be due toLsupporting an off-center load with the hook. in either case, the presenti-nvention eliminates such feed-back of torsional loads by the provisionof means for locking the wrist automatically before the hoot: or hand isoperated, and before any .appreciable torsional load can be developedtherein.

Another object of the invention is to provide a novel mechanism forartificial arms, wherein the lock for locking-fthe wrist unit againstrotation is operated hy the same control member that is used to operatethe hook or hand. The advantage of this arrangement is that iteliminates the need for utilizing another of the amputees f limitedsupply oi control movements to operate the wrist lock, and thus makesanother control movement available to perform some other usefulfunction. One of the features of the invention is that the forcerequired to operate the lock is substantially less than the forcerequiredV to operate the hoo-h, and therefore the lock can be lockedwithout actually opening the hook.

Stili a further object of the invention is to provide an artificial armwith rotatable wrist for below-elbow amputees that is so constructed andarranged as to make possible a more compact Wrist. unit andsmaller-sized forearm than has heretofore been obtainable. This has thedualadvantage ci providingv an arm capable of accommodating the longestforearm stump' Short of wrist disarticulation, 'and at the same timeproriding an arm more nearly approxiinatingA the dimensions andproportions of the natural arm. lThese objects are realized by providinga forearin, member made up of a stationary rearshell and a rotatableouterY shell; while mounted. on the Adistal end' of the latter is, thewrist unit carrying the nook or hand.l The: rotatable outer shell isrigid-ly attached to the stump socket, so that the two rotate as asingle unit. A pair of lines are attached tothe wrist atcircumferentially spaced points thereon and pass around two adjacentpulleys on the `rotatable outer shell,v then extend backup the arm-,andaround another two pulleys to circumierentially spaced points ofattachment with the stationary rear shell.

The diameter ofthe stationary rear shell is approximately twice thediameter of the wrist unit, and thereforerotation of the outer shellwith respect to the stationary yshell causes the lines to be paid out.and taken up.v at the upper ond at twice the rate they vare taken up.and paid out, respectively, at the lower end. As a result, the wristuni-t is turned on the rotatable outer snel-l through an angulardistance equal to. twice the angular traelofv the outer shell relativetov the stationary upper shell. The net result is a 3:1 step-up oi therotational movement transmitted from the stump socket to the wrist unit.

To. lock the wrist unit against rotation, a locking member is pivoted onthe rotatable outer shell and is engageable with teeth on the wristunit. The locking member is normally springheld out oiengagement withthe said teeth, and is pulled into locking engagement by a slidingoperator on the outer forearm shell. The flexible conduit housing of theBowden cable control member that operates the hook or hand is attachedat its lower end to the sliding operator, and the. reaction force on thehousing when a control force is applied to the cable, causes theoperator to slide in they direction to lock the wrist. The forcerequired to overcome friction and the spring-pressure acting on thelocking member,` is substantially less than the force required to openthe noch and therefore the wrist is locked before the hook opened.

The foregoing and other objects and advantages of the .present inventionwill become apparent to those Skilled in the art unon consideration ofthe following detailed description of the preferred embodiment thereof,reference being had 'to the accompanying drawings, wherein:

Figure 1 is a top plan View of an arm embodying the principles of myinvention;

Figure 2 is a bottom View of the same;

Figure 3 is a longitudinal sectional View, taken along the line 3 3 inFigure l, showing the wrist lock in the locked condition;

Figure 4 is an enlarged transverse sectional view through the Wrist,taken at 4 4 in Figure 3; and

Figure 5 is an enlarged fragmentary View of the wrist lock mechanismshown in Figure 3, with the locking device depicted in the unlockedcondition.

As brought out earlier in this specification, the arm of the presentinvention is for the belowelbow amputee whose stump has sufcient lengthand mobility about the pronation-supination axis to permit of its use inthe function of pronating and supinating the hand or hook. Accordfingly, the arm is comprised of a forearm member Ill, which is connectedby an elbow joint to a leather cuff |2 that is fastened around the upperarm of the amputee. Strap loops I3 and buckles i4 are provided onopposite sides of the cuff |2 for attachment to a suitable shoulderharness (not shown) which serves to hold the artificial arm in place.The elbow joint is of the conventional type for below-elbow arms, and ismade up of two laterally spaced hinge connections l5, which are normallydisposed on opposite sides of the natural elbow and coaxial therewith.The forearm member l0 is seen to comprise a stationary rear shell 20, onwhich is mounted a rotatable outer shell 2|, and carried by the latteris a wrist unit 22 to which a terminal device, such as a hook 23 orhand, is attached.

Both the rear shell 20 and outer shell 2| are preferably formed bylaminating several layers of plastic-impregnated cotton stockinet overplaster forms of the desired shape, and then curing or polymerizing theresin in an oven to produce an extremely strong, durable, andlightweight structure. In the process of fabricating the shells 25 and2|, various metal fittings such as the components of the elbow hingeconnection l5, as well as an outer ball race 24, cooperating inner race25, and wrist unit body member 26 are embedded in the plastic laminateand become permanently bonded thereto. Balls 28 run in the races 24, 25,and provide a frictionless bearing for rotatably supporting the outershell 2| on the rear shell 20.

Riveted or otherwise fixed to the inside surface of the inner race 25 isa stump socket 3D, which is also preferably formed by laminatingplastic-impregnated cotton stockinet over a plaster model of the stump,and then curing the same to provide an accurately formed socket that isexactly shaped to receive the stump. The stump socket 35 is thusattached to the outer shell 2| and is therefore rotatable therewith, andit is by the rotation of the outer shell 2| relative to the stationaryrear shell 20 that the stepped-up rotation of the wrist member 22 iseffected.

The wrist unit body member 25 has a cylindrical opening 3| provided inthe center thereof, and at each end of the opening are circumferen--tial grooves that form the outer raceways for two rows of ball bearings32 and 33. The inner raceways for the balls 32, 33 are formed in twocooperating members 34 and 35, which are screwthreaded together to makeup the rotatable portion of the wrist unit. The member 34 consists of atubular body 36 with a radial flange 31 at the back end thereof; theinner surface of the body portion 36 being threaded for a portion of itslength to receive the screwthreaded shank 40 of the hook or hand 23.

The right hand end of the member 35, as seen in Figures y3 and 5, isenlarged in diameter and provided with a radial flange 4|, forming acup-like cavity 42 that receives a rubber washer 43. The washer 43 isengaged on its outer face and compressed against the bottom of thecavity 42 by a metal ring 44 having a spherically curved, annular seat45 that receives a correspondingly curved, annular enlargement 46 on thestem of the hook 23. This arrangement permits the ring 44 yto be drawnup tightly against the washer 45 without turning relative thereto whenthe hook is screwed into the threaded portion of member 36. Thecompression of the rubber washer 43 takes up any clearance between thethreads of the stem 40 and member 36, and makes for a tight connectionbetween the hook and the wrist unit.

Projecting radially outward from the flange 4| around the circumferencethereof is an annular ridge 50 having a pulley groove 5| formed therein.Two cords 52 and 52 are trained in opposite directions through thepulley groove 5l from the bottom sideA thereof, and the ends of thecords are attached to the inner raceway 35 in any suitable manner. Thetwo cords 52, 52 pass around and extend rearwardly from two pulleys 53,53 (Figure 4) that are journalled on opposite sides of a boss 54projecting downwardly from the bottom of the wrist unit body member 26.The two cords pass through holes 55 (Figure 4) in the end of the member26 and extend back along the arm through a cable housing 56 on theinterior of the shell 2|.

At the back end of the shell 2|, the cords emerge through holes 60 andpass in opposite directions around two laterally spaced pulleys 6|, 6|'that are journalled on the bottom side of the inner race member 25.After passing around the pulleys 6|, 6|', the two cords 52, 52 extendcircumferentially around the arm in opposite directions to points ofattachment 62 and 52 with the stationary rear shell 2li; the latterbeing cut out and provi-ded with a metal insert 63 for the purpose.

It will be noted in Figure 2 that the diameter of the shell 2B at thepoint of attachment of cords 52, 52' is approximately twice the diameterof the pulley groove 5I, which means that for a given angular incrementof rotation of the shell 2| relative to the shell 2U, the length of cordtaken up over one of the pulleys 6|, El and payed out over the otherwill be twice the length payed out and taken up over the correspondingpulleys 53, 53,' at the other end of the shell. This vpull exerted onone cord and slackening off of the other causes the wrist members 34, 35to rotate through an angular distance equal to twice the angular travelof the shell 2| relative to the stationary shell 20, i. e., at a 2:1ratio. Since the inner raceway 34, 35 is mounted on the shell 2|, italso turns with the latter, and the step-up ratio is thereby increasedIto 3:1. Other step-up ratios can be obtained-of course, by varying therelative diametral proportions of the shell 2U and pulley groove 5|,although the aeesgeoe in the: cas-e of the typical external controlhookillustrated, or they may result from lifting loads. which areoit-centery :fromv the. axis or rotation of the hook'. In either caseythe .-teedbaclr. ot torsional loads ten-ds to twist the stump- .soc-keton.

the stump, `causing much discenario-rt'.V to the` amputee. y

The automatic locking .means ,iustreterred yto c'omprisesa p-ivotedlooking dog havinga tooth 61 which is` engageable with a toothedportionz ori-the back side of the ridgemem-ber 580i part 35.,

The dog ed is disposed. between two laterally spacedlugs te projectingupwardly from the .topv of the wrist unit body. member .2.6, andistie-urnalled for rocking movement abouta pinlextending transverselythrough Yahmed..holes in the.

severalparts. Theouter `end of the` dog .65 is. slotted to receive oneend. of alink. 11.andthe two parts are connected .by a pin '12.. Thelink "H extendsrearwardlythrough. a. hole 1.3 in the end ofmernberl 25,andv its backend is connected to a sliding operator M.

The operator 'M is in the form oa .cable housing anchor and to this endis. providedwith an. internally threaded hole 15 into-whichaspiringwound Bowden cable housing, or conduit JB, 'is'.`

screw threaded. .A exible. tension-transmitting cable 80 passes throughthe. housing'l .and is freely sldable therein.; .the .bottomv of thecable being attached by a fitting 8i to the. thumb 8:2 of the hoolr. Thecable. and housingextend around the arm ina longspirabas shownin-Figures .l and 2, and the housing. is attached. to the leather-cuirl2. by aA iixed anchorftting 83. A terminal Afitting Bil is attached tothe top end of the cab-le Si), and this is secured to the usual shoulderharness in the well known manner.

The operator 'lli is slidably supportedon a plate S6 which is rivetedover an opening'll inthe outer shell 2l. A slot Si extending lengthwiseof the arm is for-med .in the .plate 8S, and a threaded stem 92 of theoperator extends down through this slot. A nut 93 is screwed onto thethreaded stud 92, and the rear end of link 'H iits over the endv of thenut and is secured thereto. rlihe operator lf3 is thus free to slidelengthwise of `thearm within the limits of the slot 9i, and in so doing,rocks the locking dog i between the locked position shown in Figure 3and the unlocked position shown in Figure v5;

The locking dog c5 is urged in clockwise direction (Figure 5) to theunlocked position by means of a wire spring t5, best shown in Fig-ure 4,which engages the pin l2. Coils 9S of the spring are wrapped around .pin'l I, and the ends of the vspring are vsuitably attached tothe wristunit'body member 2G.

When a pull is applied to vthe Acontrol cable te, the latter tends tostraighten'out, but is constrained `against so doing bythe anchor.iitting 83 and' operator l, which vare attached to :the cable housing.Fitting f8.3 is rigidly xed position on the lcuff it, and therefore isimmovable, but the operator 'lll is movable `within the limits o-- theslot 9 l, andthereforetends to be pushed down to therouter end thereof.As the operator .moves outwardly, orto theright, as vewedinFigures-B-6'.. and. 5, the :link 1 t :swings the flocking dog, ES; in. a clockwise'direction against, the: pressure ofy spring.

95:-,` ta the locking;position .shown in Figure .In

this position, the tooth Bil' is engaged. between. two of the teeth 68on the wristv member 35, and the latter is thereby preventediromrotating with respect to the outer shell 2l.

The strength: of the spring .S51-is. such that a lpull of .approximatelytwopounds on the control. cable 8G is required to.v operate the lock,Whereas the tension of the rubber bands 9i on the hooknecessitates: aminimum pull or at least six pounds. to open the hook.; `Thisrelationship insures that the wrist will be locked. before the .hook isopened, and' also.: enables; the: amputee to lock the wrist,y evenWithout-operating the. hook', by merely applating-.tension on thecontrol cable 80 sufficient to operate the lock', but not enough toopenthe hook. This-gives the hook `stability' for lifting oli-center loads,and prevents any torsional feedback tothe 'stump socket.

rvAnother advantage of the artincial arm of my invention is that thearrangement of one -ro-w `of ballbearings 28 near `the back end of theforearm member permitsa reduction inthe overall size of the torearm,vand also makes possible a shorter wrist unit, .so that it can be .usedon the longest forearm .stump short of wrist. disarticulation. Ari--other-.consideration is the pleasing appearanceof the arm, which closelyfollows the 'shape` and size of a.. .natural arm, besides beingrelatively freel fro-m. protuberancesancl sharp edges that cause unduewear of the clothing. In this connection, it Will be noted. that Atheypulleys Si, 6I are covered by a cover plate 98 (Figure 2), vhile theouter, or distal end of the outer shell `2l is covered by a plasticl cap9S that. vencloses the wrist drive and wrist lock Amechanisn'i.

While. I have sho-wn and described in considerable detail what I believeto be the preferred form of my invention, itis to be understood thatsuch details are merely illustrative, and that various changes may bemade in the. shape and arrangement of. the .several parts, withoutdeparting from the vbroad scope of the'inyentiom as dened in theappended claims.

I claim:

1. In an artiiicial arm having a forearm memmer, a stump socketrotatably mounted on said forearm member, a wrist member rotatablymounted on said forearm member, and a terminal device attached to saidWrist member, the combination of driving means connecting said stumpsocket with said wrist member, a locking dog. on. said forearm membermovable into engagement with. said wrist member to lock the saineagainst rotation, a control cable operably connected to .said terminaldevice, a housing enclosing said. cable, and an operating memberslidably mounted Yon said forearm member and connected. to said lockingdog, said cable housing being attached to said .operating member, andsaid operating member being operable to move said locking dog intoengagement with said wrist member when at one extremity of its traveland to` .disengage said locking dog therefrom when at theotherextremity, said operating `member being shifted to said one extremity bythereaction force on said cable housing when a force is applied to thecable so as to lock said wrist when said terminal device is beingoperated.

2. 1nv an artificial -armhavinga forearm member, a wrist memberrotatablymounted thereon, and a terminal device attached to .said wristmember, the combination vof a locking lmember mounted .on said Yforearmmemberfor movement into engagement With said wrist member to lock thesame against rotation, a control member operably connected to saidterminal device, and an operating member on said forearm memberconnected to said control member in a manner to be shifted thereby whena force is transmitted to said terminal device, said operating memberbeing connected to said locking member to move the same into engagementwith said wrist member, so as to lock said Wrist while said terminaldevice is being operated.

3. In an articial arm having a forearm member, a Wrist member rotatablymounted thereon, and a terminal device attached to said wrist member,the combination of a locking member mounted on said forearm member formovement into engagement with said Wrist member to lock the same againstrotation, a control cable operably connected to said terminal device, ahousing enclosing said cable, and an operating member movably mounted onsaid forearm member and connected to said locking member to shift thesame into engagement with said wrist member when moved in one direction,said cable housing being attached to said operating member,

and the latter being moved in said one direction by the reaction forceon said cable housing when a force is applied to the cable so as to locksaid wrist when said terminal device is being operated.

4. In an artificial arm having a forearm member, a wrist memberrotatably mounted thereon, and a terminal device attached to said wristmember, the combination of a locking member mounted on said forearmmember for movement into engagement with said wrist member to lock thesame against rotation, a control member operably connected to saidterminal device, and an operating member movably mounted on said forearmmember, said operating member being connected to said locking member tomove the same into engagement with said wrist member when shifted in onedirection, and said operating member being connected to said controlmember in a manner to be shifted thereby in said one direction when aforce is transmitted by said control member to said terminal device,whereby said wrist is locked While said terminal device is beingoperated.

5. In an articial arm having a forearm member, a wrist member rotatablymounted thereon, and a terminal device attached to said wrist member,the combination of a locking member pivoted on said forearm member forrocking movement into and out of engagement with said wrist member tolock the same against rotation, a spring yieldingly urging said lockingmember out of engagement With said wrist member, a control cableoperably connected to said terminal device, a housing enclosing saidcable, an operating member slidably mounted on said forearm member andattached to said cable housing, and a link connecting said operatingmember to said locking member, whereby the latter is rocked intoengagement with said wrist member against the pressure of said spring bysliding movement of said operating member in one direction, saidoperating member being shifted in said one direction by the reactionforce on said cable housing when a force is applied to the cable so asto lock said wrist when said terminal device is being operated.

6. In a below-elbow arm, the combination of a stationary forearm shellhaving an outer shell mounted on the outer end thereof for rotationabout the longitudinal aXis of the forearm, a stump socket attached tosaid outer shell and ro- 8 tatable therewith, al Wrist member rotatablymounted on said outer shell coaxial therewith, and a pair of flexiblelines carried by said outer shell, said lines being connected at one endto' 'said stationary forearm shell and at the other end to said Wristmember in a manner whereby rotation of said outer shell with respect tosaid stationary shell causes a pull to be exerted on one of said lines,and the pull of said one line causes said wrist member to be rotated inthe same direction relative to said outer shell.

'7. In a below-elbow arm, the combination of a stationary forearm shellhaving an outer shell rotatably mounted thereon, a stump socket attachedto said outer shell and rotatable therewith, a. wrist member rotatablymounted on said outer shell, a pair of flexible lines extendinggenerally lengthwise of said outer shell, a pair of pulleys journaled onsaid outer shell at the proximal end thereof, and another pair ofpulleys journaled on said outer shell at the dista1 end thereof, theinner ends of said lines passing around said first-named pulleys andextending circumferentially around the arm in opposite directions topoints of attachment with said stationary forearm shell, the outer endsof said lines passing around said last-named pulleys and eX- tending inthe same directions as their respective inner ends to points ofattachment with said Wrist member, whereby rotation of said outer shellwith respect to said stationary shell causes a pull to be exerted on oneof said lines, and the pull of said one line causes said Wrist member tobe rotated in the same direction relative to said outer shell.

8. A below-elbow artificial arm comprising a stationary forearm shell,an outer shell rotatably mounted thereon, a stump socket attached tosaid outer shell and rotatable therewith, a wrist member rotatablymounted on said outer shell and adapted to receive a terminal device,means operable to rotate said Wrist member relative to said outer shellwhen the latter is rotated by said stump socket relative to saidstationary shell, a locking member mounted on said outer shell formovement into and out of engagement with said wrist member to lock thesame against rotation,

a control member connected to said terminal de-Y vice, and an actuatingmember associated with said control member and movable thereby `to shiftsaid locking member into engagement with said wrist member, so as tolock said wrist member while said terminal device is being operated.

9. A below-elbow articial arm comprising a stationary forearm shell, anouter shell rotatably mounted thereon, a stump socket attached to saidouter shell and rotatable therewith, a wrist member rotatably mounted onsaid outer shell and adapted to receive a terminal device, a pair offlexible lines carried by said outer shell, said lines being connectedat one end to said stationary forearm shell and at the other end to saidWrist member in a manner whereby rotation of said outer shell withrespect to said stationary shell causes a pull to be exerted on one ofsaid lines, and the pull on said one line causes said wrist member to berotated in the same direction relative to said outer shell, a lockingmember mounted on said outer shell for movement into and out ofengagement with said Wrist member to lock the same against rotation, acontrol member operably connected to said terminal device, and anoperating member movably mounted on said'outer shell, said operatingmember being connected to said locking member to move the same intoengagement with said wrist member when shifted in one direction, andsaid operating member being shifted in said one direction responsive tothe application of a force on said control member, whereby said wrist islocked while said terminal device is being operated.

l0. A below-elbow artificial arm comprising a stationary forearm shell,an outer shell rotatably mounted thereon, a stump socket attached tosaid outer shell and rotatable therewith, a wris member rotatablymounted on said outer shell and adapted to receive a terminal device, apair of iexible lines carried by said outer shell, said lines beingconnected at one end to said stationary forearm shell and at the otherend to said wrist member in a manner whereby rotation oi said outershell with respect to said stationary shell causes a pull to be exertedon one of said lines, and the pull on said one line causes said wristmember to be rotated in the same direction relative to said outer shell,a locking member mounted on said outer shell for movement into and outof engagement with said wrist member to look the same against rotation,a control cable operably connected to said terminal device, a housingenclosing said cable, and an operating member slidably mounted on saidouter shell and connected to said locking member to shift the same intoengagement with said wrist member when moved in one direction, saidcable housing being attached to said operating member, and the latterbeing moved in said one direction by the reaction force on said cablehousing when a force is applied to the cable so as to lock said wristwhen said terminal device is being operated.

ll. In a below-elbow artificial the combination of a stationary forearmshell having an outer shell rotatably mounted thereon, a stump socketattached to said outer shell and rotatable therewith, a wrist memberrotatably mounted on said outer shell and adapted to receive a terminaldevice, a pair of flexible lines extending generally lengthwise of saidouter shell, a pair of pulleys journaled on said outer shell at theproximal end thereof, and another pair of pulleys journaled on saidouter shell at the distal end thereof, the inner ends of said linespassing around said rst-named pulleys and extending circumferentiallyaround the arm in opposite directions to points of attachment with saidstationary forearm shell, the outer ends of said lines passing aroundsaid last-named pulleys and extending in the same directions as theirrespective inner ends to points of attachment with said wrist member,whereby rotation of said' outer shell with respect to said stationaryshell causes a pull to be exerted on one of said lines, and the pull ofsaid one line causes said wrist member to be rotated in the samedirection relative to said outer shell, a locking member mounted on-said outer shell for movement into engagement with said wrist member tolock the same against rotation, a control member operably connected tosaid terminal device, and an operating member movably mounted on saidouter shell, said operating member being connected to said lochingmember to move the same into engagement with said wrist member whenshifted in one direction, and said operating member being shifted insaid one direction responsive to the application of a force on saidcontrol member, whereby said wrist is locked while said terminal deviceis being operated.

l2. In a below-elbow artificial arm, the combination of a stationaryforearm shell having an outer' shell rotatably mounted thereon, a stumpsocket attached to said outer shell and rotatable therewith, a wristmember rotatably mounted on saidv outer shell and adapted to receive aterminal device, a pair of flexible lines extending generally lengthwiseof said outer shell, a pair of pulleys journaled on said outer shell atthe proximal end thereof, and another pair of pulleys journaled on saidouter shell at the distal end thereof, the inner ends of said linespassing around said first-named pulleys and extending circumferentiallyaround the arm in opposite directions to points of attachment with saidstationary forearm shell, the outer ends of said lines passing aroundsaid last-named pulleys and extending in the same directions as theirrespective inner ends to points of attachment with said wrist member,whereby rotation of said outer shell with respect to said stationaryshell causes a pull to be exerted on one of said lines, and the pull ofsaid one line causes said wrist member to be rotated in the samedirection relative to said outer shell, a locking member mounted on saidouter shell for movement into engagement with said wrist member to lockthe same against rotation, a control cable operably connected to saidterminal device, a housing enclosing said cable, and an operating memberslidably mounted on said outer shell and connected to said lockingmember to shift the same into engagement with said wrist member whenmoved in one direction, said cable housing being attached to saidoperating member, and the latter being moved in said one direction bythe reaction force on said cable housing when a force is applied to thecable so as to lock said wrist when said terminal device is beingoperated.

GILBERT M. MO'IIS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,408,880 Rebers Oct. 8, 1946 2,457,316 Northrop et al Dec.28, 1948 2,493,841 Threewit Jan. 10, 1950 FOREIGN PATENTS Number CountryDate 103,759 Great Britain Feb. 8, 1917 397,708 Germany June 27, 1924

